I would like a whole lot of airbenders to come out of hiding with a bunch of flying bison and lemars so that Aang, Appa and Momo are no longer the last ones of their kind and they can reform their nation.

that would give some closure.

Well, this is my theory...

There's the giant battle, with Aang and Zuko fighting Azula and firelord. Firelord is about to kill Aang, but Zuko saves him but ends up dead. The firelord gets really upset and kills Azula because she was happy and the firelord is devestated and either admits defeat or commits suicide. Then everyone gets sad and Katara tells her love for Zuko.

Aang dies at the hands of the Fire Lord (Ozai dies too). Zuko takes Katara, but leaves her and lives with his Uncle who at this point is old has gotten sick and is in depends. Katara takes care of a bunch of kids she made with Zuko alone. She grows obese and at this point her image is so disturbing the Katara we knew during the war is a relic and far cry from the past. Katara dies of heartfailure, but her kids can't do anything about it, she dies, paramedics fork lift her carcass out of the house.

Zuko starts to question himself again and realizes his inner homosexual love for Sokka. Unfortunately Sokka does not reciprocate, btw he left Suki and walked the path of a casanova. He gets STD's from all the woman he slept with and returns to find Suki has committed suicide via sepukku. Sokka dies at the hospital after the diseases get the worst of him. Zuko still alone finally finds comfort with Haru and they live together somewhat happy.

Meanwhile, Mai upset over Zuko leaving her for Katara turns to prostitution, then cuts her wrist to death and she dies with Suki (ritual suicide). Azula who was improsined thought to be too evil to contain yet too hot to kill. So they gave her a lobotomy and Ty Lee moves and takes care of her *spoon feeds Azula* They have lesbian sex and die happy. Oh and Iroh walks away in dipers running away from his home ahamed and looking for something better. He disappears from the rest of the world somewhere....